Physicians now recognize the importance and usefulness of incorporating an assessment of health-related quality of life (HRQL) in their clinical practice and clinical studies. Conventional measurements provide useful information about airway status but provide little information about functional impairments that are important in a patient's everyday life. This paper outlines the concept of HRQL and explains the importance of the concept for treating asthma patients. The paper also describes several questionnaires for measuring HRQL, including athma-specific quality of life instruments, and discusses how to select an appropriate HRQL instrument.